Many wireless communication techniques are suggested as candidates for a high-speed mobile communication. Among the candidate techniques, an Orthogonal Frequency Division Multiplexing (OFDM) scheme is recognized as a leading future-generation wireless communication technique. Wireless Metropolitan Area Network (WMAN) of Institute of Electrical and Electronics Engineers (IEEE) 802.16 is adopting the OFDM as its standard.
To raise reliability of the data transmission, wireless communication systems are making use of a Hybrid Automatic Repeat Request (HARQ) scheme which incorporates a Forward Error Correction (FEC) scheme and an Automatic Repeat Request (ARQ) scheme.
Using the HARQ scheme, a receiver corrects errors of a packet received from a transmitter through an error detecting code. Next, the receiver determines whether to request the retransmission based on the error detecting code (e.g., Cyclic Redundancy Check (CRC) code) of the error-corrected packet. When receiving a retransmission packet from the transmitter, the receiver can obtain an additional gain (e.g., coding gain and Signal to Noise Ratio (SNR) increase) by decoding the retransmission packet and the previously received packet through Increment Redundancy (IR) or Chase Combining (CC).
To use the HARQ scheme, the receiver requires a buffer for storing an initial HARQ packet. A size of the buffer can vary depending on the cost or the use of the receiver.
When failing to receive the initial transmission HARQ packet, the receiver requests the retransmission to the transmitter and receives the retransmission HARQ packet from the transmitter. Next, the receiver determines whether to concatenate the received retransmission HARQ packet after the pre-stored initial transmission HARQ packet or to combine the received retransmission HARQ packet with the initial transmission HARQ packet, or to concatenate the retransmission HARQ packet in a certain region after the initial transmission HARQ packet and combine the remaining part with the front part of the initial transmission HARQ packet.
In general, the transmitter generates a codeword by encoding the encoding packet at a Mother Code Rate (MCR) and transmits HARQ packets by splitting the codeword to the HARQ packets according to the HARQ scheme. Correspondingly, as combining or concatenating the packets, the receiver requires information relating to the MCR, the size Nep of the encoding packet, or the codeword length.
In an IEEE 802.16e standard system, a base station and a terminal carry out HARQ buffer capability negotiation prior to the data transmission so as to support the buffer of various sizes. For example, the terminal informs the base station of the HARQ buffer capability including Nep_max information and Aggregation (Ag) information. Herein, Nep_max indicates a maximum data amount storable per HARQ channel and Ag indicates whether the buffer of the other HARQ channel is usable or not. For example, when the number of the HARQ channels is ‘4’, the buffer size for each HARQ channel is ‘100’, and the Ag field is set to ‘on’, the base station can transmit data of the maximum size ‘100’. The terminal can store the data of the maximum size ‘400’ using four buffers.
The base station and the terminal determine the Nep_max value according to the storage capability of the buffer of the terminal. That is, the base station enables the communication in consideration of the buffer of the terminal by encoding and transmitting data of the smaller size than Nep_max. When a considerable data throughput is required, the base station and the terminal set the Ag field to ‘on’. Accordingly, the base station is able to transmit data in the greater size than Nep_max. The terminal can also store data in the size greater than Nep_max using a plurality of buffers for the multiple HARQ channels.
As discussed above, when one HARQ channel occupies the buffer for another HARQ channel, the terminal cannot receive data of a new HARQ channel until the operation for the corresponding HARQ channel is finished. Additionally, since the total size of the buffers of the terminal is limited, the data length transmittable from the base station to the terminal is restricted although the Ag field is set to ‘on’. Thus, a novel method is required to support a high data throughput without interrupting a new HARQ channel.